A used ski binding must have the characteristics agreed in the private sale. If the seller expressly promised a safe or fully functional binding and a dangerous defect appears, that promise is a central issue. Describing the item as used does not answer the question on its own.
Under section 922 of the Austrian Civil Code, the seller is responsible for the item matching the contract and being fit for the agreed or ordinarily expected use. For a ski binding, the listing, messages, visible condition and intended use must be read together. A warranty exclusion has to be assessed in that context.
This post concerns the private purchase of a used binding. Material breakage in an owner's product and evidence preservation are covered in the post on product liability after binding material failure. A rental shop follows a different legal framework, explained in the post on ski rental and binding setting.